The technology available today in edge and surface finishing and conditioning goes far beyond simply removing unwanted bits of metal for cosmetic purposes (although this is still important). Today it is known that controlled, consistent edge/surface finishing can dramatically improve product performance and life. Removing stress risers at sharp corners by producing controlled radii on edges can substantially improve thermal and mechanical fatigue strength of highly stressed components. Improved surface integrity produced by processes that either remove tensionally stressed surfaces, such as those remaining after thermal machining methods, or impart compressive stresses in their own right, can again improve fatigue strength of components.
Improved surface finishes (and radii) in passages through which gas or fluids will flow reduce boundary layer turbulence and improve flow rates. Improved surfaces and edges on gears improve service life and power transmission efficiency. The seemingly minute work that is being done on surfaces and edges--if done consistently by an automatic process--can improve the strength, reliability, service life or performance of the product being manufactured.
There are several major automatic finishing processes, some of these include abrasive flow finishing, thermal deburring blast finishing, vibratory finishing, centrifugal burrel finishing, electrochemical deburring radiusing, and chemical deburring. Some processes are selective, some are not; some are good at finishing internal areas, some are not; some require special tooling, others none; some involve measurable consumables costs, others practically none; most polish and radius while removing burrs, some don't; some involve a substantial investment in equipment; others are fairly inexpensive.
In the process of chemical deburring, a burr-containing workpiece is immersed in a corrosive medium which attacks the burrs and consumes them. For purposes of this discussion and the claims of this application, the term "burr" is intended to mean an undesirable projection of material that results from a cutting, forming, blanking or shearing process.
In most instances, chemical attack of the entire surface of the workpiece occurs and is frequently undesirable. To provide protection for these surfaces it is possible to mask-off those portions of the workpiece which are to be protected from the corrosive solution leaving only the unmasked portions, i.e., burrs, exposed to corrosive attack. However, the masking and unmasking of selected portions of a workpiece is a time consuming and expensive operation which rules out the use of chemical deburring especially in the case of workpieces with close tolerances or dimensions or workpieces in which internal surfaces are to be deburred. The process of the present invention is adaptable to all types of workpieces and is especially useful in situations with close tolerances or dimensions or for internal surfaces.
Many of the maskants which are known to the art are not soluble in the corrosive medium which attacks the burrs. Such a maskant is disclosed in U.S. Pat. No. 4,023,998 which describes the use of a protective foil or layer, which can consist of metal or plastic, to protect a thin metal layer in a laminate through which holes have been drilled. When the laminate is chemically treated to remove the burrs which form due to drilling, the metal foil which is not attacked, prevents the thin metal layer from dissolving as well.
U.S Pat. No. 4,023,998 also discloses, as an alternative, the use of a chemical agent which attacks the burr material more rapidly than it attacks the material in the protective foil or layer, indicating the protective layer may be soluble in the corrosive medium.
U.S. Pat. No. 3,741,804 discloses the formation of a protective layer of ice on a workpiece which is then chemically deburred. The low mass burrs are warmed by an aqueous metal-corroding medium which then melts the protective ice layer, exposing the burrs to selective attack by the corroding medium.
The present invention differs from that dislcosed in U.S. Pat. No. 4,023,998 in that the maskant is soluble in the corrosive medium, the maskant is not a protective foil, and the process is not limited to use on laminates used for printed wiring. The process of the present invention is adaptable to workpieces of all shapes and sizes and is especially useful for workpieces intricate detailing or close tolerances. The process of the present invention is also useful for deburring or milling internal surfaces or internal edges of workpieces. It would be difficult to apply a protective foil to most internal surfaces of any but the simplest workpieces.
The present invention is a marked improvement over that disclosed in U.S. Pat. No. 3,741,804 in that the maskant is more stable than ice and no refrigeration step is necessary. Using the process of the present invention, workpieces can be masked and then chemically deburred at some later time without loss of the maskant during the waiting period.